Radiant heat apparatus



R. BARTON RADIANT HEAT APPAR ATUS Filed Dec: 2, 1929 Patented Dec. 13, 1932 rarest caries ROGER BARTON, OF CHICAGO, ILLINOIS RADIANT amt APPARATUS Application filed December 2, 1929. Serial No. 411,194. v i

The principalobject of this invention is to provide a simple instrument for use in studying radiant energy in the visible and infra red spectra, and, in general, of heat radiation,

which objectis admirably accomplished by the combination of a thermopile including a plurality of couples and a reflector which collects and concentrates heat on the-hot junctions of the thermopile.

vention will be revealed as'the description'is read in connection with the accompanying drawing illustrating thepreferred emb0di-- the correspondingly specific description, is to.

. V be taken in a limiting sense, for they are used for the purpose of disclosure only, and it is intended that the substanceof the invention shall be covered by the appended claims irrespective of the particular disclosure, I

The apparatus illustrated in Fig. 1 includes a thermopile, generally indicated by A, a collecting reflector and casing, generally indicated by B, and a galvanometer, generally indicated by G. The thermopile may, of course, he made of a variety of metals selected from the thermoelectric series, and also-alloys of metals in that series. and some of the metallic sulphides. such as galena. From this list it will be sufficient to mention iron, constantan, bis- 'muth, nickel, German silver, lead, platinum,

copper, zinc, antimony, tellurium and selenium. The relative merits of these various substances are well known. and the selection of any two will be based upon the particular 45 object that may be attained by the peculiarities of a. couple made of them.

speaking, No. wire. or the equivalent in strips, willbe found satisfactory in an estimate of the general nature illustrated in the drawing.

Further objects and advantages of theini line normal to the Generally Preferably,'and as illustrated, the thermopile is composed of a plurality ofv strips 10 and 11, of iron and constantan;respectively, having the ends overlapping andsp'ot welded at 12 innumbers suflicient tofform approximatelyBS hot and cold junctions. Such/a thermopile will develop about 50-inicrovolts 7 per degree of-temp'erature' difference for each couple; thus the total M. F. developed per degree is of the order of 2 millivolts. On; the assumptionthat the resistance is of the order of 30 ohms, and that the galvanometerf has approximately the same resistance, the current perdegre'e'elevation of temperature of the hot junctions is in the neighborhood of 32 microamperes. The galvanometer mentioned is sensitive enough to indicate .0004 of this current, hence atemperature elevation of the thotf junctions of around .0004 degrees centigrade will be. discernible.'

The end strips I ofipthe thermopile are equipped with lead wires-13, for connection with binding posts 14 Y The reflector and casing is composed of two similar aluminium die castings 15 and 16, 'securedtogether by bolts 17 passing through flanges 18.

' The reflecting surface 19 is, for the want of a better term, called cylindro-parabolic, because in this preferred form it is conceived as a'surface generated by a right line moving parallel to itself along a parabolic path,

whereby the foci of the reflecting surface are in a right line 20, in which the hot junctions of the thermopile A may be located. 0

Another way of viewing the reflecting surface is such that all sections parallel to that shown in Fig. 2 are parabolas with foci in a plane in which the section is taken.

However, this cylindro-parabolic form is notindispensable, for theoretically, at least, a surface in which a transverse section would be curved, or in which the focal points would be on a curve, would also'be suitable.

Adjacent to the right end and externally of the reflecting surface 19, as shown in Figs. 1 and 2. the castings 15 and 16 are cored out to form a cavity 21, which communicates with the horn-like aperture bounded by the reflecting surface and side walls through a narrow slot 22 in which the thermopile is clamped.

The strips 10 and 11 forming the thermopile are held in a frame made of two celluloid strips 23, corresponding surfaces of which have been softened by treating them -.with a solvent such as acetone or ether, and

then pressed together against opposite sides of the thermopile. This gives the thermopile a stability not inherent in the fine strips, and provides a convenient surface for'clamping between the separate-castings to hold the hot junctions in properrelation to the ..:foc al line. Y I I The cavity 21,? when rthe'ireflector made of aluminum: unli ed. with: aluminum, or

v some metal having'a likehigh'degree of conductivity, serves theimpoiftant'i function of protecting the 'tcold; junctions from undesired thermal influences, But though the deadair space within the cavityintroduces a "thermal lag before temperature changes in the reflector canaflect the cold junctions, and is a convenience in making electrical connections to the thermopile,.itj-iollows that the cavity may be omitted and-the entire thermopile with the exception of the exposed hot junctions. may. be 'rigidly .clamped between the two halves of the reflector. q g v The lower casting 16 is equipped with a handle 24, by which the instrument maybe handled or clamped to a suitably fixed support in the laboratory.

The construction of the thermopileand its mounting arrangements follow sound physical principles of design. The thermopile itself hassmall thermal capacity and smallv heat conductivity away from the junctions.

' The hot junctions are desirablyblackened tire area are so concentrated that the net intensification, with losses for absorption deducted, is about twenty times. Theactual temperature of the cold junctions can if. necessary be determined, but in ordinary-use they are assumed to he at room temperature.

The thermal capacity of the reflector 1s so great that no significant change in tempera-. ture will take place while any ordinary ob? servation is being made. y

Aluminum alloys in common use are espe cially suited for use in the casing because they lend themselvcs'to die casting. present an eflicient reflecting surface and have apmaterials,"including copper, cuprous alloys,

propriate conductivity; but a variety of other i and the non-corrosive ferrous alloys,.are obolas having foci in line, said reflector hav-- ing a narrow slot adjacent to the foci, and a thermopile including a. plurality of fhot. points mounted in said slot.

2. In a device of the class described, 9. casing including a reflector composed of many like conic sections with their foci in line, a cavity spaced from the reflector and connected with it by a narrow slot, and a thermopile composed'of a plurality of couples mounted in the slot with their hot junctions in line with the foci and their cold junctions in the cavity. Y

3. A device sensitive to radiant heat comprising a reflector having a multiplicity of foci arranged in a line, a thermopile having itshot junctions arranged to occupy the line of the foci and having its cold junctions located behind the reflecting surface and in thermal relation to the body of the reflector.

4., A device sensitive to radiant energy comprising a split cylindro-parabolic reflector having clamping faces located at the vertices of the parabolas, a thermopile having its hot junctions occupying the line of the foci at the parabolas clamped between the two parts of the reflector and having its cold junctions in thermal relation to the clamping faces. 4

. 5. A heat concentrating casing for radiant heat apparatushaving a cavity in which the opposedwalls are substantially straight in" normal to the planes of said longitudinal sections, and means associated with the casing,

adapted to support a thermopile with its hot junctions coincident with the line focus of the parabolic sections. and an extensionin the rear part of the casing having. a separate w cavity adapted to house the cold junctions of the thermopile.

6. In a device of the class described, a re flector having a reflecting surface in which parallel sections are parabolas having foci in a line and a thermo-counle, the hot junctions of which are coincident with said line and the cold junctions of which are located externally of said reflecting surface in thermal relation to the bodv of the reflector and out of line of the heat rays falling on said reflecting surface.

7'.- In a device of the class described. a casing including a reflector having a reflecting surfacecomnosed of manv like conic sections with their foci in a line and a thermocouple composed of a plurality of couples having memes 

